With a continuous increase of a wireless communication data rate and a user quantity, frequencies and bandwidths of a wireless communications system also increase continuously. In addition, a communications system has been developed from a second generation (2G) wireless communications system into 3G and 4G communications systems.
The 2G wireless communications system mainly uses 900 MHz and 1.8 GHz frequency bands, with a channel bandwidth generally ranging from hundreds of hertz to thousands of hertz. The 3G communications system mainly uses multiple frequency bands of 2 GHz or lower than 2 GHz, with a channel bandwidth generally being several megahertz; and the 4G communications system mainly uses several frequency bands lower than 4 GHz, with a channel bandwidth generally ranging from tens of megahertz to hundreds of megahertz.
In a data transmission process, an existing communications system performs receiving, processing, and transmitting by using a separate antenna and a separate radio-frequency link on multiple different frequency bands, and antennas and radio-frequency links of the multiple frequency bands are basically separate. Therefore, to develop high frequencies and large bandwidths, the communications system requires more radio-frequency link components. For example, an available frequency band of a next-generation 5G mobile communications system may be up to 3 GHz to 100 GHz or even wider. Therefore, when performing data transmission, the next-generation 5G mobile communications system requires a large quantity of radio-frequency link components to complete the data transmission, which causes an overlarge link size of a high-frequency large-bandwidth communications system.